Detection of blockage in a porous member

ABSTRACT

A method of detecting at least a partial blockage in a porous member separating an inner chamber of a device having a gas sensor responsive to an analyte positioned within the inner chamber and an ambient environment includes emitting pressure waves within the inner chamber and measuring a response via a sensor responsive to pressure waves positioned within the inner chamber.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. Provisional Patent ApplicationSer. No. 62/291,823, filed Feb. 5, 2016, the disclosure of which isincorporated herein by reference.

BACKGROUND

The following information is provided to assist the reader inunderstanding technologies disclosed below and the environment in whichsuch technologies may typically be used. The terms used herein are notintended to be limited to any particular narrow interpretation unlessclearly stated otherwise in this document. References set forth hereinmay facilitate understanding of the technologies or the backgroundthereof. The disclosure of all references cited herein are incorporatedby reference.

Many gas sensors include gas porous members/barriers or diffusionbarriers that separate or partition the analytical components of thesensor from the environment the sensor is intended to monitor. Suchporous members are commonly used to reduce or eliminate ingress ofcontaminants that may impede the operation of the sensor's analyticalcomponents and/or to isolate the analytical components as a source ofignition in the environment to which the sensor is exposed. When suchporous members are used, the analyte gas(es) to be detected/monitored bythe sensor must pass through the porous member to reach the analyticalcomponents of the sensor. The capability and effectiveness of analytetransport through the porous member directly impacts the speed,precision and accuracy with which the sensor can respond to changes inthe relative concentration of the analyte in the external, ambientenvironment being monitored. As a consequence, porous members aredesigned and/or selected such that the analyte transport through theporous member, in concert with the analytical components of the sensor,enable the sensor to respond to levels and/or changes in the relativelevels of the analyte in the monitored environment at the nominal orminimal rate, precision and accuracy defined by the sensing application.Once a sensor is deployed, extraneous contaminants (arising in thenormal operating environment or resulting from atypical events ormaintenance activities) contacting or penetrating the porous member caneither directly, or as a consequence of reaction with the porous member,inhibit analyte transport between the environment and the analyticalcomponents of the sensor. Such an inhibition in analyte transportthrough the porous member, resulting in deviation from the target sensorresponse rate to the analyte and/or deviation in precision/accuracy inassessment of absolute or relative changes in analyte concentration, isdesignated by the term “blockage” or “blocking”. Additionally, thecontaminant or condition causing the blocking is commonly referred to asthe “blockage”. A common example of blockage occurs in industrialenvironments where sensor response to the analyte can become partiallyor completely inhibited by overpainting, water, dirt/mud, insect oranimal deposits, or by other extraneous diffusion-impeding substances.Failure to identify impairment of transport through the sensor porousmember can result in under-detection or non-detection of analyteconcentration levels exceeding safe environmental limits.

In addition to blockage of a diffusion or other sensor porous member,performance of the sensor itself may degrade over time. Prudence thusdictates that gas detection instrumentation be tested regularly forfunctionality. It is a common practice to, for example, perform a “bumpcheck,” or functionality check on portable gas detection instrumentationon a daily basis. The purpose of this test is to ensure thefunctionality of the entire gas detection system, commonly referred toas an instrument. A periodic bump check or functionality check may alsobe performed on a permanent gas detection instrument to, for example,extend the period between full calibrations. Gas detection systemsinclude at least one gas sensor, electronic circuitry and a power supplyto drive the sensor, interpret its response and display its response tothe user. The systems further include a housing to enclose and protectsuch components. A bump check typically includes: a) applying a gas ofinterest (usually the target gas or the analyte gas which the instrumentis intended to detect); b) collecting and interpreting the sensorresponse; and c) indicating to the end user the functional state of thesystem (that is, whether or not the instrument is properly functioning).

As described above, such bump tests are performed regularly and,typically, daily for portable gas detection instruments. Bump checksprovide a relatively high degree of assurance to the user that the gasdetection device is working properly. The bump check exercises all thenecessary functionalities of all parts of the gas detection device inthe same manner necessary to detect an alarm level of a hazardous gas.In that regard, the bump check ensures that there is efficient gasdelivery from the outside of the instrument, through any transport paths(including, for example, any protection and/or diffusion member ormembranes) to contact the active sensor components. The bump check alsoensures that the detection aspect of the sensor itself is workingproperly and that the sensor provides the proper response function orsignal. The bump check further ensures that the sensor is properlyconnected to its associated power supply and electronic circuitry andthat the sensor signal is interpreted properly. Moreover, the bump checkensures that the indicator(s) or user interface(s) (for example, adisplay and/or an annunciation functionality) of the gas detectioninstrument is/are functioning as intended.

However, a periodic/daily bump check requirement has a number ofsignificant drawbacks. For example, such bump checks are time consuming,especially in facilities that include many gas detection systems orinstruments. The bump check also requires the use of expensive andpotentially hazardous calibration gases (that is, the analyte gas or asimulant therefor to which the sensor is responsive). Further, the bumpcheck also requires a specialized gas delivery system, usually includinga pressurized gas bottle, a pressure reducing regulator, and tubing andadapters to correctly supply the calibration gas to the instrument. Therequirement of a specialized gas delivery system often means that theopportunity to bump check a personal gas detection device is limited inplace and time by the availability of the gas delivery equipment.

Recently, a number of systems and methods have been proposed to reducethe number of bump tests required. Such systems may, for example,include electronic interrogation of a sensor and/or a test of thetransport path to the sensor, including through a diffusion or otherbarrier (without application of an analyte gas or a simulant therefor).Nonetheless, it remains desirable to develop improved testing systemsand methodologies for reducing the number of bump checks required forsensors.

SUMMARY

In one aspect, a method of detecting at least a partial blockage in aporous member separating an inner chamber of a device having a gassensor responsive to an analyte positioned within the inner chamber andan ambient environment includes emitting pressure waves within the innerchamber and measuring a response via a sensor responsive to pressurewaves positioned within the inner chamber. Emitting pressure waveswithin the inner chamber may, for example, include activating a speakerpositioned within the inner chamber (to, for example, emit acousticwaves). Measuring the response via the sensor responsive to pressurewaves may, for example, include measuring the response via a microphonepositioned within the inner chamber. In a number of embodiments,pressure waves are emitted at a plurality of frequencies within thechamber and a response is measured at more than one of the plurality offrequencies.

Measuring a response may, for example, include measuring at least one oftransmission, reflection or absorbance (of the pressure waves). At leastone of a change in amplitude and a change in phase may, for example, bemeasured. In a number of embodiments, a change in phase is measured. Ina number of embodiments, each of a change in amplitude and a change inphase is measured. A lock-in algorithm may, for example, be used tomeasure each of the change in amplitude and the change in phase. Phaseand amplitude may, for example, be measured at each of a plurality offrequencies of the emitted pressure waves.

At least one of the plurality of frequencies of the emitted pressurewaves may, for example, be a self-resonant frequency of the porousmember, and a response measured at that frequency may be associable witha blockage that infiltrates pores of the porous membrane. A measuredresponse may, for example, be used to discriminate between at least apartial blockage associated with an outside surface of the porous memberand at least a partial blockage infiltrating pores of the porous member.

In another aspect, a gas sensor device to detect an analyte gas in anambient environment includes a housing including an inner chamber and aport, a porous member in operative connection with the port to separatethe inner chamber from the ambient environment, a sensor responsive tothe analyte positioned within the inner chamber, a source of pressurewaves positioned within the inner chamber, a sensor responsive topressure waves positioned within the inner chamber; and circuitry inoperative connection with the sensor responsive to pressure waves torelate a response of the sensor responsive to pressure waves to blockagein the porous member. The source of pressure waves may, for example,include a speaker, and the sensor responsive to pressure waves may, forexample, include a microphone. The speaker may, for example, emitacoustic waves or sound. Acoustic waves may be emitted at a plurality offrequencies.

The circuitry may, for example, measure at least one of transmission,reflection or absorbance of the pressure waves. In a number ofembodiments, the circuitry measures at least one of a change inamplitude and a change in phase. The circuitry may, for example, measurea change in phase. In a number of embodiments, the circuitry measureseach of a change in amplitude and a change in phase. Each of a change inphase and a change in amplitude may be measured at more than one of theplurality of frequencies of the emitted pressure waves.

The circuitry may, for example, include a processor system in operativeconnection with a memory system. The memory system may, for example,include a lock-in algorithm executable by the processing system tomeasure each of the change in amplitude and the change in phase.

At least one of a plurality of frequencies of emitted pressure wavesmay, for example, be a self-resonant frequency of the porous member, anda response measured at the at least one of the plurality of frequenciesmay be associable with a blockage that infiltrates pores of the porousmembrane. The circuitry may, for example, be adapted to use the measuredresponse to discriminate between at least a partial blockage associatedwith an outside surface of the porous member and at least a partialblockage infiltrating pores of the porous member.

In another aspect, a method of detecting at least a partial blockage ina porous member separating an inner chamber of a device having a gassensor responsive to an analyte positioned within the inner chamber andan ambient environment includes emitting pressure waves within the innerchamber and measuring a change in phase of a response via a sensorresponsive to pressure waves. The change in phase of the response may,for example, be measured via the sensor responsive to pressure waveswhich is positioned within or located within the inner chamber. Themethod may further include measuring a change in magnitude of theresponse. In a number of embodiments, the change in phase of theresponse is measured at more than one frequency. In a number ofembodiments, the change in phase and the change in magnitude of theresponse are measured at more than one frequency.

Measuring the response may, for example, include measuring at least oneof transmission, reflection or absorbance. In a number of embodiments, alock-in algorithm is used to measure each of the change in amplitude andthe change in phase. At least one of the more than one frequency may,for example, be a self-resonant frequency of the porous member and aresponse measured at the at least one of the more than one frequency maybe associable with a blockage that infiltrates pores of the porousmembrane.

The method may further include using the measured response todiscriminate between at least a partial blockage associated with anoutside surface of the porous member and at least a partial blockageinfiltrating pores of the porous member. Pressure waves may, forexample, be emitted at a self-resonant frequency of the porous memberand a response measured at the self-resonant frequency may be associatedwith a determination of the at least a partial blockage infiltratingpores of the porous membrane.

In another aspect, a gas sensor device to detect an analyte gas in anambient environment includes a housing including an inner chamber and aport, a porous member in operative connection with the port to separatethe inner chamber from the ambient environment, a sensor responsive tothe analyte gas positioned within the inner chamber, a source ofpressure waves positioned within the inner chamber, a sensor responsiveto pressure waves, and circuitry in operative connection with the sensorresponsive to pressure waves to relate a phase response of the sensorresponsive to pressure waves to blockage in the porous member. Thesensor responsive to pressure waves may be positioned within the innerchamber. The circuitry may also be adapted to further effect otheractions and/or functions as described herein.

In another aspect, a method of detecting at least a partial blockage ina porous member separating an inner chamber of a device having a gassensor responsive to an analyte positioned within the inner chamber andan ambient environment includes emitting pressure waves within the innerchamber and measuring a change in a response at more than one frequencyvia a sensor responsive to pressure waves. The change in the responsemay, for example, be measured via the sensor responsive to pressurewaves which is located within or positioned within the inner chamber. Achange in phase of the response may be measured at each frequency. In anumber of embodiments, a change in magnitude of the response is measuredat each frequency. In a number of embodiments, a change in phase and achange in magnitude of the response are measured at each frequency.

Measuring the response comprises measuring at least one of transmission,reflection or absorbance. In a number of embodiments, a lock-inalgorithm is used to measure each of the change in amplitude and thechange in phase. At least one of the more than one frequency may, forexample, be a self-resonant frequency of the porous member and aresponse measured at the at least one of the more than one frequency maybe associable with a blockage that infiltrates pores of the porousmembrane.

In another aspect, a gas sensor device to detect an analyte gas in anambient environment includes a housing including an inner chamber and aport, a porous member in operative connection with the port to separatethe inner chamber from the ambient environment, a sensor responsive tothe analyte positioned within the inner chamber, a source of pressurewaves positioned within the inner chamber adapted to emit pressure wavesat more than one frequency, a sensor responsive to pressure waves andcircuitry in operative connection with the sensor responsive to pressurewaves to relate a response of the sensor responsive to pressure waves ateach of the more than one frequency to blockage in the porous member.The sensor responsive to pressure waves may be positioned within theinner chamber. The circuitry may also be adapted to further effect otheractions and/or functions as described herein.

In another aspect, a method of detecting at least a partial blockage ina porous member separating an inner volume of a device and a volumeoutside the device includes emitting pressure waves within the innerchamber and measuring a change in phase of a response via a sensorresponsive to pressure waves. In general, the methods and devicesdescribed herein may be used to detect at least a partial blockage inany device or system including a porous member.

In another aspect, a device includes a housing having an inner chamberand a port, a porous member in operative connection with the port toseparate the inner chamber from the ambient environment, a source ofpressure waves positioned within the inner chamber, a sensor responsiveto pressure waves, and circuitry in operative connection with the sensorresponsive to pressure waves to relate a phase response of the sensorresponsive to pressure waves to blockage in the porous member. Thesensor responsive to pressure waves may be positioned within the innerchamber. The circuitry may also be adapted to further effect otheractions and/or functions as described herein.

In a further aspect, a method of detecting at least a partial blockagein a porous member separating an inner volume of a device and a volumeoutside the device includes emitting pressure waves within the innerchamber and measuring a change in response at more than one frequencyvia a sensor responsive to pressure waves positioned within the innerchamber. In a number of embodiments, a change in phase of the responseis measured at each frequency. In a number of embodiments, a change inmagnitude of the response is measured at each frequency. In a number ofembodiments, a change in phase and a change in magnitude of the responseare measured at each frequency.

In still a further aspect, a device, includes a housing having an innerchamber and a port, a porous member in operative connection with theport to separate the inner chamber from the ambient environment, asource of pressure waves positioned within the inner chamber adapted toemit pressure waves at more than one frequency, a sensor responsive topressure waves, and circuitry in operative connection with the sensorresponsive to pressure waves to relate a response of the sensorresponsive to pressure waves at each of the more than one frequency toblockage in the porous member. The sensor responsive to pressure wavesmay be positioned within the inner chamber. The circuitry may also beadapted to further effect other actions and/or functions as describedherein.

The present devices, systems, and methods, along with the attributes andattendant advantages thereof, will best be appreciated and understood inview of the following detailed description taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an embodiment of a gas sensor device hereof.

FIG. 2 illustrates another embodiment of a gas sensor device hereof

FIG. 3 illustrates pressure or audio sensor response over a range offrequencies for a blocked and unblocked porous metal frit in the sensorof FIG. 2.

FIG. 4 illustrates another embodiment of a gas sensor device hereof.

FIG. 5 illustrates pressure or acoustic sensor response over a range offrequencies for a blocked and unblocked porous metal frit in the sensorof FIG. 4.

FIG. 6 illustrates an embodiment of a test system used to study gassensor devices as illustrated in FIG. 4.

FIG. 7 illustrates reflection coefficient amplitude change over a rangeof blockage percent for the porous metal frit of the gas sensor deviceof FIG. 4.

FIG. 8 illustrates reflection coefficient phase change over a range ofblockage percent for the porous metal frit of the gas sensor device ofFIG. 4.

FIG. 9A illustrates schematically the transmission (T), reflectance (R)and absorbance (A) of sound in a membrane or frit in the presence of ablockage.

FIG. 9B illustrates an energy balance block diagram of acoustic wavesincident to a porous member such as a frit.

FIG. 9C illustrates a polar plot setting forth vector addition ofreceived signals.

FIG. 9D illustrates a polar plot setting forth components of a receivedsignal change in the presence of an external blockage.

FIG. 9E illustrates a representative example of blockage classificationand classification errors utilizing a single parameter (change inreflection magnitude) at a single interrogation frequency (500 Hz).

FIG. 9F illustrates a representative blockage classification usingmagnitude response at multiple interrogation frequencies demonstratedfor the case of 20% and 60% blockage with frequency dependentthresholding.

FIG. 9G illustrates a representative blockage classification using phaseresponse at multiple interrogation frequencies demonstrated for the caseof 20% and 60% blockage with frequency dependent thresholding.

FIG. 9H illustrates a representative polar plot combining magnitude andphase at three interrogation frequencies for 20% and 60% blockagewherein the shaded areas demonstrate the application of the detectionzones identified in FIG. 9E applied to the blockage detection case at 3kHz.

FIG. 9I illustrates a block diagram setting forth a representativeembodiment of a methodology for discrimination of blockage caused byobstruction on an outside of a porous member.

FIG. 10A illustrates transmission coefficient change in the case of ducttape blockage of the porous metal frit of the gas sensor device of FIG.4 over a range of frequencies.

FIG. 10B illustrates reflection coefficient change in the case of ducttape blockage of the porous metal frit of the gas sensor device of FIG.4 over a range of frequencies.

FIG. 10C illustrates absorption coefficient change in the case of ducttape blockage of the porous metal frit of the gas sensor device of FIG.4 over a range of frequencies.

FIG. 11A illustrates transmission coefficient change in the case of iceblockage of the porous metal frit of the gas sensor device of FIG. 4over a range of frequencies.

FIG. 11B illustrates reflection coefficient change in the case of iceblockage of the porous metal frit of the gas sensor device of FIG. 4over a range of frequencies.

FIG. 11C illustrates absorption coefficient change in the case of iceblockage of the porous metal frit of the gas sensor device of FIG. 4over a range of frequencies.

FIG. 11D illustrates a phase shift of a wave traveling through a fritwhich occurs in the presence of an ice blockage.

FIG. 12A illustrates transmission coefficient change in the case of saltblockage of the porous metal frit of the gas sensor device of FIG. 4over a range of frequencies.

FIG. 12B illustrates reflection coefficient change in the case of saltblockage of the porous metal frit of the gas sensor device of FIG. 4over a range of frequencies.

FIG. 12C illustrates absorption coefficient change in the case of saltblockage of the porous metal frit of the gas sensor device of FIG. 4over a range of frequencies.

FIG. 13A illustrates a block diagram of an embodiment of a system andmethodology for discrimination of acoustic changes originating from theporous member using one or more natural resonant frequencies of theporous member that block transmission wherein the porous member isunobstructed by internal contaminants.

FIG. 13B illustrates a block diagram of an embodiment of a system andmethodology for discrimination of acoustic changes originating from theporous member using one or more natural resonant frequencies of theporous member that block transmission showing changes in reflected andreturned signal resulting from impedance changes (for example, shifts ininternal resonant frequencies) resulting invasive contamination of thefrit.

FIG. 14 illustrates the frequency dependence of the reflectancecoefficient in a study showing the change in acoustic energy reflectedto the receiver at a resonant frequency of approximately 6.5 kHz as aresult of contamination (infiltration) of the pores of a porous member(frit).

FIG. 15A illustrates a block diagram of an embodiment of a system andmethodology for enhanced resonant frequency monitoring facilitated byselection of geometry of chamber coupled to the porous member andspeaker/microphone port geometry using an internal resonance chamber.

FIG. 15B illustrates a block diagram of an embodiment of a system andmethodology for enhanced resonant frequency monitoring facilitated byselection of geometry of chamber coupled to the porous member andspeaker/microphone port geometry with the addition of external resonancechamber.

FIG. 16 illustrates a block diagram of an embodiment of a system andmethodology for transmission detection of a blockage showing principalacoustic signal propagation for a non-blocked condition.

FIG. 17A illustrates a block diagram of an embodiment of a system andmethodology for transmission detection of a blockage showing obstructionbetween the porous member and the receiver.

FIG. 17B illustrates a block diagram of an embodiment of a system andmethodology for transmission detection of a blockage showing obstructionon an opposite side of the receiver from the porous member.

DETAILED DESCRIPTION

It will be readily understood that the components of the embodiments, asgenerally described and illustrated in the figures herein, may bearranged and designed in a wide variety of different configurations inaddition to the described representative embodiments. Thus, thefollowing more detailed description of the representative embodiments,as illustrated in the figures, is not intended to limit the scope of theembodiments, as claimed, but is merely illustrative of representativeembodiments.

Reference throughout this specification to “one embodiment” or “anembodiment” (or the like) means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment. Thus, the appearance of the phrases “in oneembodiment” or “in an embodiment” or the like in various placesthroughout this specification are not necessarily all referring to thesame embodiment.

Furthermore, described features, structures, or characteristics may becombined in any suitable manner in one or more embodiments. In thefollowing description, numerous specific details are provided to give athorough understanding of various embodiments. One skilled in therelevant art will recognize, however, that the various embodiments canbe practiced without one or more of the specific details, or with othermethods, components, materials, et cetera. In other instances, wellknown structures, materials, or operations are not shown or described indetail to avoid obfuscation.

As used herein and in the appended claims, the singular forms “a,” “an”,and “the” include plural references unless the context clearly dictatesotherwise. Thus, for example, reference to “a sensor” includes aplurality of such sensors and equivalents thereof known to those skilledin the art, and so forth, and reference to “the sensor” is a referenceto one or more such sensors and equivalents thereof known to thoseskilled in the art, and so forth. Recitation of ranges of values hereinare merely intended to serve as a shorthand method of referringindividually to each separate value falling within the range. Unlessotherwise indicated herein, and each separate value, as well asintermediate ranges, are incorporated into the specification as ifindividually recited herein. All methods described herein can beperformed in any suitable order unless otherwise indicated herein orotherwise clearly contraindicated by the text.

As used herein, the term “circuit” or “circuitry” includes. but is notlimited to, hardware, firmware, software or combinations of each toperform a function(s) or an action(s). For example, based on a desiredfeature or need. a circuit may include a software controlledmicroprocessor, discrete logic such as an application specificintegrated circuit (ASIC), or other programmed logic device. A circuitmay also be fully embodied as software.

The term “control system” or “controller,” as used herein includes, butis not limited to, any circuit or device that coordinates and controlsthe operation of one or more input or output devices. For example, acontroller can include a device having one or more processors,microprocessors, or central processing units (CPUs) capable of beingprogrammed to perform input or output functions.

The term “processor,” as used herein includes, but is not limited to,one or more processor systems or stand-alone processors, such asmicroprocessors, microcontrollers, central processing units (CPUs), anddigital signal processors (DSPs), in any combination. A processor may beassociated with various other circuits that support operation of theprocessor, such as a memory system (for example, random access memory(RAM), read-only memory (ROM), programmable read-only memory (PROM),erasable programmable read only memory (EPROM)), clocks, decoders,memory controllers, or interrupt controllers, etc. These supportcircuits may be internal or external to the processor or its associatedelectronic packaging. The support circuits are in operativecommunication with the processor. The support circuits are notnecessarily shown separate from the processor in block diagrams or otherdrawings.

As a metric, blockage may directly designate impedance of analytetransport through the porous member and/or designate the consequentialchanges in sensor performance resulting from this transport impedance.Blockage may, for example, be metered in a continuous measure. Forexample, blockage may be metered as a percentage, ranging from 0% whenanalyte transport through the porous member is normal or nominal to 100%marking total inhibition of analyte transport between the sensoranalytical components and the monitored environment. Blockage may alsobe metered as discrete states with designations such as unblocked(indicating typical or normal analyte transport through the porousmember) or partial (indicating impedance of analyte transport beyondtypical or normal but less than complete transport inhibition) orcomplete (indicating total inhibition of analyte transport through theporous member). Alternatively, blockage can be ascribed to booleanstates, with an unblocked state indicating inhibition of analytetransport through the porous member falls below a designated acceptablelimit, and a blocked state indicating analyte transport inhibitionexceeds the designated limit. Adequate measure in detecting anddesignating blockage (and/or resultant impairment to sensor performance)is important for assurance of sensor function. As describe above,failure to identify impairment of transport through the sensor porousmember can result in under-detection or non-detection of analyteconcentration levels exceeding safe environmental limits.

In a number of embodiments, devices, systems and methods hereof are usedto detect flow through a porous member, membrane or barrier (forexample, a diffusion barrier) of, for example, a sensor for detecting atarget or an analyte gas. Such porous members may, for example, beporous metal frits or porous polymeric membranes in a number ofrepresentative embodiments. In a number of embodiments, a source,generator or transmitter of pressure waves or acoustic waves such as aspeaker is played into a volume or chamber behind (that is, on thesensor side and opposite the ambient side) of a porous member such as aporous frit or a porous membrane. A response to the generatedacoustic/pressure waves (for example, sound) is measured by a pressurewave sensor, acoustic sensor or receiver such as a microphone and isrelated to gas transport through the membrane. In general, any sensor orreceiver that is responsive to pressure changes or waves of pressurepropagated in a medium (for example, air) may be used herein. Suchsensors or receivers are sometimes referred to herein generally asacoustic sensors or receivers.

The present devices, systems and methods may, for example, be used infixed or portable gas instruments, but are particularly beneficial infixed gas instruments. In the case of a fixed (as opposed to portable)gas instrument, the instrument is calibrated when it is put intoservice. As described above, after placement in service, it isrecommended to frequently “bump test” the instrument to check for gasflow to the sensor and that the sensor responds as expected. As alsodescribed above, to bump test an instrument, the user applies atarget/analyte gas (or a simulant gas to which the sensor is responsive)of a known concentration to the instrument and checks the instrument foran expected or acceptable response. If the sensor response is acceptable(using, for example, predetermined thresholds), the user can thencalibrate the instrument to the known concentration of the target gas.

Using electronic interrogation systems and methods as described, forexample, in U.S. Pat. Nos. 7,413,645, 7,959,777 and U.S. PatentApplication Publication Nos. 2014/0273263, 2013/0193004, 2013/0192332,2013/0186776, 2013/0186777, and U.S. patent application Ser. No.15/012,919, the disclosures of which are incorporated herein byreference, one has the ability to electronically interrogate a sensor,determine changes in sensor performance thereby, and compensate sensoroutput so that the sensor response is acceptable, thereby extending theperiod of time between (or eliminating) bump checks. Electronicinterrogation of a sensor may, for example, include applying electricalenergy to an electrode or sensor element and measuring a response to theapplication of electrical energy and/or an electrical property of theelectrode or sensor element to determine a state of the sensor.Electronically interrogating a sensor, however, cannot account for ordetect blockage of the porous member that separates/protects the sensorfrom the ambient environment or outside world. Combining electronicinterrogation of the sensor with systems, devices and methods ofdetecting blockage of such a porous member, provides the ability tofurther reduce or eliminate bump testing the instrument.

In a number of representative embodiments hereof, to detect a blockageof a porous member separating a gas sensor from the ambient environment(in which the concentration of the analyte gas it to be determined) anacoustic wave or waves transmitted from a source/speaker interacts withthe porous member and with any blockage thereof. Signals are thenreceived by an acoustic sensor/microphone. The response is processed andcorrelated to a loss in flow through the porous member and/or, in thecase of a sensor, a loss in gas response of the sensor. There are anumber of ways to analyze and/or to process the data to determine thepresence and/or degree of a blockage. In a number of embodiments, thesource/speaker and the acoustic sensor are positioned or located on thesame side of the porous member as the gas sensor.

In a number of studied embodiments hereof, a combustible gas sensordevice 100 was tested which included a sensor 110 within an innerchamber 120 created by an explosion-proof housing 130 and a porousmember in the form of a porous frit 140. Catalytic combustible gassensor devices and electronic interrogation thereof are, for example,described in U.S. Patent Application Publication No. 2014/0273263, thedisclosure of which is incorporated herein by reference. Althoughcombustible gas sensors were studied in a number of representativeembodiments hereof, the devices, systems and method hereof can be usedin connection with any sensor (for example, electrochemical sensors,photoacoustic sensors, etc.) or other device in which a porous member ormembrane separates an inner chamber or volume from an outsideenvironment. In the embodiment of device 10, a speaker 150 and amicrophone 160 are also positioned within chamber 120. It is notnecessary to acoustically isolate speaker 150 and microphone 160 fromthe remainder of inner chamber 120 and sensor 110 or to narrowly channelthe propagation of acoustic/pressure waves therebetween. In theillustrated embodiment, sensor 110, speaker 150 and microphone 160 arein electrical connection with circuitry including a printed circuitboard 170 which may be in electrical connection with control circuitry180 illustrated schematically in FIG. 1, which may be positioned withinand/or outside of explosion proof housing 130. Control circuitry 180 mayfor example, include a processor system 190 (including one or moreprocessors such as microprocessors) and a memory system 194 in operativeconnection with processor system 190. Memory system 194 may, forexample, include one or more algorithms stored therein and executable byprocessor system 190.

As illustrated, for example, in FIG. 1, acoustic waves propagate withinchamber 120 toward frit 140. Without limitation to any mechanism, someof the acoustic waves pass into frit 140, and some of the sound wavesare reflected back into inner chamber 120. In that regard, of theacoustic waves that pass into frit 140, some are absorbed in frit 140,some are reflected back into inner chamber 130 (from which the acousticwaves emanated), and some pass through frit 140 into the ambientenvironment outside of explosion proof housing 130. The acoustic wavesthat are passed through frit 140 and outside of explosion-proof housing130 are “lost” acoustic waves, which are very relevant to the degree ofblockage of frit 140. When frit 140 is blocked, less acoustic waves (forexample, sound waves) are lost, and more acoustic waves are reflectedback into chamber 120. In a number of studies, multiple frequencies weregenerated by speaker 150. If, for example, one looks at what sound isreceived by microphone 160 in the frequency domain, one should be ableto readily pick out the frequencies that were generated. Once can thenset a threshold at each frequency for a magnitude and/or phase for whata blocked or unblocked response should be. Analysis may also be made inthe time domain (wherein thresholds may, for example, be set for amagnitude and/or time delay of a response). In the time domain, adriving force including multiple frequencies may, for example, begenerated by the speaker.

In experiments with generating various frequencies and measuring theresponse on microphone 160, it was unexpectedly discovered that at somefrequencies the response was actually quieter/decreased when frit 140was blocked. It was also found that the resonances of chamber 120 may besignificant, and in the same frequency region as the interrogationsignal.

To address resonances within the inner chamber, a combustible gas sensordevice 100 a, illustrated without a housing in FIG. 2, was manufacturedwherein a speaker 150 a and microphone 160 a were positioned within achannel or channels 132 a in acoustic connection with chamber 130 abetween frit 140 a and sensor 110 a. It was found that sound pressurelevel (SPL) received by microphone 160 a and also the SPL directed atfrit 140 a were increased as compared to combustible gas sensor device100. Because the SPL was increased, the signal response was increasedbetween a blocked and an unblocked state. FIG. 3 shows data from arepresentative response vs. frequency study for a blocked frit, anunblocked frit, and an open frit (that is, the absence of a frit).

Combustible gas sensor device 100 a did not exhibit the resonancesexperienced with combustible gas sensor device 100 and, as indicatedabove, exhibited a greater difference in the response from a blocked toan unblocked state. A disadvantage of the design of combustible gassensor device 100 b, however, is difficulty of manufacture.

In device 100 b of FIG. 4, speaker 150 b and microphone 160 b werepositioned adjacent or on printed circuit board 170 b. A control systemincluding a microprocessor 190 b and memory 194 b was also incorporatedon printed circuit board 170 b to control the system and executecomputations required to detect blockage. Unlike device 100, however,speaker 150 b and microphone 160 b were ported directly to a volume ofchamber 130 b between sensor 110 b and frit 140 b via channels 132 b and134 b, respectively. The design of device 100 b of FIG. 4 decreased thevolume of chamber 130 b within which sensor 110 b, microphone 150 b, andspeaker 160 b were positioned (as compared to device 100 of FIG. 1),while significantly improving manufacturability as compared to device100 a of FIG. 2. The smaller chamber of device 100 b provided a numberof advantages over the case in which porting was not used. In thatregard, sensor response was faster because less air had to be exchangedwith the ambient air that was being monitored. Furthermore, the volume(loudness) of the signal from speaker 150 b that was received bymicrophone 160 was increased because speaker 150 b had to drive asmaller volume chamber. FIG. 5 illustrates the difference in reflectancecoefficient amplitude response between a frit 140 b blocked with paintand an unblocked frit 140 b over a range of frequencies, with frequencyon the x-axis and the magnitude of the measured response on the y-axis.

Based on the design of device 100 b of FIG. 4, a test system 100 b′(illustrated schematically in FIG. 6) was constructed in which differentfrits 140 b, with and without various types of blockage, could bereadily placed in operative connection with test system 100 b′ andremoved from connection therewith. Test system 100 b′ further includes asecond acoustic sensor/microphone 164 b positioned outside of frit 140b. The measured output from test system 100 b′ included changes in thephase and magnitude response of the transmission coefficient (measuredby microphone 164 b), reflection coefficient (measured by microphone 160b) and absorption coefficient (calculated). Systems hereof may measurereflected energy and/or transmitted energy. Measuring reflected energyalone provides the benefit of use of an acoustic sensor or microphoneonly within the enclosure of a device. Further, in the case of, forexample, a sensor used in environments where hazardous, combustibleand/or explosive gases may be present, enclosure of the acoustic sensorwithin an explosion proof housing eliminates a potential ignitionsource. However, intrinsically safe circuitry and/or additionalprotection may be used for an acoustic sensor or microphone placedoutside of a porous member in environments in which hazardous,combustible and/or explosive gases may be present.

In a number of studies, reflectance and/or transmission were measured atone or more frequencies for each tested frit 140 b. FIGS. 7 and 8,respectively, illustrate representative magnitude and phase response forvarious blockage types at a frequency of 500 Hz. Although informationregarding blockage of frit 140 b can be obtained from changes in eitherphase or magnitude of, for example, measured reflectance and/ortransmission data. It has been discovered that it may be beneficial toanalyze each of phase and magnitude. In that regard, at a particularfrequency, a certain type of blockage may cause a significant change inmagnitude and very little or no change in phase. Similarly, at aparticular frequency, a certain type of blockage may cause a significantchange in phase and very little or no change in magnitude.

FIG. 9A illustrates schematically the transmission (T), reflectance (R)and absorbance (A) of acoustic waves/sound interacting with a porousmember such as a frit in the presence of a blockage. In FIG. 9A, Irepresents an incident wave (arising from, for example, a speaker) tothe frit (or other porous member) and R₁, R₂, and R₃ are the reflectedwaves at the surface of the frit, at the top of the frit, and at theblockage, respectively. T represents the transmitted wave and Arepresents the absorbed wave.

In a number of embodiments hereof, a total or combined reflected waveR=R₁+R₂+R₃ is measured. The following equation describes how R₁ relatesto the incident wave: R₁≈I*Γ₁ where Γ₁ is the reflection coefficient ofthe frit to chamber border. The reflection coefficient is frequencydependent and contains phase and amplitude information. The followingequation describes how R₂ relates to the incident wave: R₂≈I*(1−Γ₁)*Γ₂,wherein Γ₂ is the reflection coefficient of the frit to air/blockageborder. Similarly, R₃ relates to the incident wave in the followingequation: R₃≈I*(1−Γ₁)*(1−Γ₂)*Γ₃, wherein Γ₃ is the reflectioncoefficient of a blockage/environmental element spaced from the frit.The total reflected wave measured at a microphone hereof takes intoaccount all three reflected waves.

FIG. 9B depicts another schematic illustration of an embodiment of aretroreflective acoustic interrogation system hereof to assess changesin acoustic properties of a porous member or barrier and/or changes inthe acoustic reflection on the side opposite the acoustic wave source ortransmitter and the acoustic wave sensor or receiver, which areindicative of the introduction or presence of an obstruction orblockage. As described above, a retroreflective system is particularlyadvantageous in situations where placement of the transmitter and/orreceiver on opposite sides of the porous member or barrier is difficultor dangerous.

The operation of such system may be discussed using acoustic energybalance principles that dictate that the sum of the energy transmittedthrough, reflected from and absorbed within a closed boundary is equalto the sum of energy/power generated within and/or incident on thatboundary. This principle is useful in describing the propagation of theacoustic interrogation signal generated from the acoustic wave source ortransmitter back to the acoustic wave sensor or receiver. Consideringseparate boundaries drawn about the transmitter and receiver, thefraction of acoustic energy that is returned to the receiver from thetransmitter is divided between the sum of the reflected and returnedenergy resultant from sound incident on the porous member and theacoustic energy that propagates to the receiver but does not impingeupon the porous member. The non-incident path acoustic energy isunmodified by the acoustic impedance of the porous member or thesurroundings on the opposite side of the porous member and thus containslittle to no information about these. A fraction of the acoustic energyreturned to the receiver from the sound incident upon the porous memberincludes the vector sum of the energy reflected by the porous member andthe energy that takes the circuitous path through the porous member tothe surroundings on the outside of the porous member and is reflectedback to the porous member and then transmitted back through the porousmember to the receiver. The amplitude and phase of the reflected energyresults mostly from the acoustic impedance (expressed in the reflectioncoefficient Rcoef) of the porous member and thus contains informationprimarily related to the porous member. The amplitude and phase of theacoustic energy returned from the surroundings on the outside of theporous member is impacted twice by the acoustic impedance of the porousmember (expressed in transmission coefficient Tcoef) and the compositeimpedance of the surroundings (expressed in Rscatter_coef), and thuscontains composite information about the porous member and surroundings.

FIG. 9C illustrates a graphical vector summation of the signalcomponents returned to the receiver resulting in the composite receivedsignal using the transmitter amplitude and phase as a reference. Themagnitudes and phases of these vectors are frequency dependent and thusthe composite sum results in a received signal with frequency dependentmagnitude and phase. The vector components with the greatest magnitudeand/or greatest phase deviation impact the magnitude and phase of thecomposite received signal most. As illustrated in FIG. 9D, thenon-incident acoustic signal returned to the receiver is unaffected bychanges in the acoustic impedance of the porous member or thesurroundings beyond the porous member and therefore contains negligibleinformation relevant to blockage detection. This suggests an acousticdesign strategy that maximizes the incident fraction of transmitterpower while minimizing the fraction propagating in the non-incident pathto maximize the magnitude and impact of information bearing signals onthe composite received signal while minimizing the impact and influence(noise) of the information deficient, non-incident signal.

The acoustic interrogation system utilizes correlation of changes in theamplitude and/or phase of the transmitter acoustic energy returned tothe receiver with changes in gas permeability through the frit and/orcombined frit and external obstructions to infer changes in restrictionof gas transport (blockage) from external surroundings to/from thetransmitter/receiver side of the frit. Because the acoustic impedance(and related transmission, reflection and absorption coefficients) ofthe porous member and external obstructions is frequency dependent, forthe purposes of blockage detection, one may select interrogationfrequencies that maximize the difference in reflection and/or returnedsound amplitude and/or phase between blocked and unblocked conditions.Such frequencies are readily determined via, for example, routineexperimental characterization of a porous member as described herein at,for example, the time of manufacture. The percentage of blockage can beinferred or a Boolean blocked state declared based on the magnitudeand/or phase change relative to the reference magnitudes and/or phasesof the unblocked system. The polar plot in FIG. 9D illustrates resultantchanges in the magnitude and phase of the received signal resulting fromthe returned and reflected vector changes resulting from an externalobstruction.

In a number of embodiments, blockage detection is significantly improvedby utilizing both magnitude and phase changes of the received signal ata single or at multiple frequencies to create a multidimensionalthreshold scheme for discerning the blockage state of the porous member.Use of a singular threshold, for example reflection magnitude, at asingle frequency can result in blockage detection errors as illustratedin FIG. 9E. Similar to FIG. 7, in FIG. 9E, the change in reflection at500 Hz with different blockage materials applied to the porous member isplotted against the resultant measured percent blockage. The horizontalBlockage Threshold line at 30% blockage represents a detection target.In the representative example of FIG. 9E, a blockage above 30% isdetermined to be blocked (with, for example, an alert of anoperator/operator system), while a blockage below this threshold isdetermined to not be blocked. In this single frequency, single thresholdschema, blockage is detected using the vertical Magnitude DetectionThreshold value. Changes in reflection magnitude exceeding thisthreshold are determined to be blocked while those falling below thethreshold are determined not to be blocked. As illustrated, thissingular threshold approach gives rise to detection errors as some ofthe blockage materials exhibit reflection magnitude changes exceedingthe threshold when blockage is below 30% (Type 1 error) while somematerials exhibit reflection magnitude changes falling below thedetection threshold when blockage exceeds 30% (Type 2 error). It isdesirable to avoid Type 1 errors as such errors could result indetermination/alert of a fault and/or initiation of a maintenance cycleto clear or repair a blockage that is not significant. It is alsodesirable to avoid Type 2 errors as such error could lead to the failureto determine/alert of a fault for a blocked porous member (indicatingthat flow through the porous member is not significantly impeded) when apotentially impairing blockage exists.

FIGS. 9F through 9H illustrates the use of both magnitude and phase datafrom three separate interrogation frequencies to discern the differencein a 20% blockage and 60% blockage. FIGS. 9F and 9G demonstrate thechange in magnitude and phase for 20% and 60% blockages with therespective thresholds at each frequency superimposed. The blockagestatus would have been determined/alerted incorrectly (Type 1 error) hadonly the magnitude responses at 500 Hz and 1 kHz been utilized in thedetection. Assuming the detection scheme requires the magnitudes of allinterrogation frequencies to exceed their respective magnitudethresholds to determine/alert the porous member to be blocked, theinclusion of the additional magnitude at 3 kHz would result in thecorrect declaration of no blockage. FIG. 9I illustrates a polar view ofthe combined magnitude and phase thresholding with the detectionboundaries at 3 kHz superimposed to further illustrate the use ofcombined response thresholds to reduce false classification anddeclaration of the blockage state of the porous member.

Blockage discrimination assesses the source of the detected blockage(that is, an obstruction/blockage external to the porous member or anobstruction/blockage arising from internal contamination/infiltration ofthe pores of the porous member) by utilizing frequencies at which thecomposite receiver signal is dominated by either the returned signal(blockage resulting from an external obstruction) or the reflectedsignal (blockage resulting from porous member contamination). In thecase that a blockage is sitting on the surface of a frit or other porousmembrane, an operator may, for example, clean the surface of the porous.In the case that a blockage agent has infiltrated pores of a frit orother porous member, replacement is likely required.

FIG. 9I illustrates the discrimination and assessment of a blockage orobstruction adjacent to the porous member (external obstruction). Todiscriminate between the porous member and an external obstruction asthe source of received acoustic signal change, an interrogationfrequency (or frequencies) is selected that is normally, substantiallytransparent to the porous member (that is, frequencies wheretransmission through the porous member is high and porous memberreflection and absorption are low) so that changes in the compositereceived signal are dominated by changes in the returned signalresultant from the introduction of the external blockage or obstruction.

FIG. 10A through 12C illustrates changes in the frequency dependentacoustic signal power transmitted to the surroundings,reflected/returned to the receiver and absorbed power with theintroduction of an external blockage or obstruction residing beyond theoutside surface of the porous membrane. As used in FIGS. 10A through12C, “untreated” indicates the reference case of a normal, unobstructedporous member or frit, while “treated” indicates the changes resultingfrom addition of an external blockage or obstruction. Ra represents thecomposite (reflected+returned) signal to the receiver dominated by thereflection of the obstruction and subsequently, the returned vector. Raincreases with the presence of a blockage as returned power increases asa result of reflection from the blockage. Ta represents acoustic powertransmitted through the combined porous member and any blockage. Tadecreases with blockage as a result of absorption and reflection. Alpharepresents acoustic power absorbed by a combination of the porous memberand any blockage. Alpha increases with the presence of a blockage as aresult of absorption thereby. In the case of the porous metal fritsstudied in FIGS. 10A through 12C, a natural resonance at 6.5 kHz of theuncontaminated frit increases porous member/frit absorption anddecreases frit transmission so that the composite receiver signals forthe unblocked and blocked cases are essentially identical and aredominated by the reflected signal from the porous member/frit.

FIGS. 10A, 10B and 10C, illustrate the test system transmissioncoefficient, reflection coefficient and alpha/absorption coefficientoutput, respectively, for an untreated frit 140 b and for frit 140 bblocked with duct tape. FIGS. 11A, 11B and 11C illustrate the testsystem transmission coefficient, reflection coefficient andalpha/absorption coefficient output, respectively, for an untreated frit140 b and for frit 140 b blocked with ice. FIGS. 12A, 12B and 12Cillustrates the test system transmission coefficient, reflectioncoefficient and alpha/absorption coefficient output, respectively, foran untreated frit 140 b and for frit 140 b blocked with salt. In FIG.11A through 12C, two frits 140 b were tested in each study

As illustrated in FIG. 11B, the reflection magnitude coefficient changedby approximately 20% throughout the entire frequency range tested in theice blockage studies. The reflection magnitude coefficient output isslightly different for the frits baked with salt, in which thereflection magnitude coefficient changes by about 20% at frequenciesbelow 1 kHz, but tapers off to having the same response as a clean fritat approximately 6.5 kHz. As described above, it was determined that atapproximately 6.5 kHz, frit 140 b is at a resonance and absorbs thesound near that frequency.

FIGS. 11A through 11C, for example, show the frequency dependency of theamplitude of each aspect of the frit, the transmission, the absorption,and the reflection. The reflection, when frit 140 b is untreated with ablocking agent, corresponds to about 70% of the incident signal'samplitude (see, for example, FIG. 11B or 12 B). When the frit is treatedwith a blocking agent, the reflection coefficient can approach 100%(see, for example, FIG. 12B).

FIGS. 13A and 13B illustrate discrimination and assessment of acousticchanges to frit 140 b (indicating internal contamination of a porousmember such as frit 140 b). To discriminate the porous member as thesource of received acoustic signal change (inferring a potentialblockage by contaminants in the porous member), an interrogationfrequency or set of frequencies is selected that is normally opaque tothe porous member (that is, the acoustic signal penetrating the porousmember is normally absorbed rather than transmitted therethrough) andsignificant changes in reflected power occur between a normal andcontaminated porous member. At these frequencies, the received signal isrelatively unaffected by presence or absence of obstructions at theoutside surface of the frit since only an insignificant amount ofacoustic power is transmitted to such an external obstruction andsubsequently returned to the receiver.

FIG. 14 illustrates a change (reduction) in acoustic power returned tothe receiver at a 6.5 kHz natural resonance frequency for frit 140 bresulting from a change in the acoustic impedance of the frit 140 barising from a contaminant that has soaked into or infiltrated the poresof frit 140 b. In FIG. 14 there is a significant difference at 6.5 kHzbetween the reflected power of the treated versus untreated response forcontaminated or infiltrated frit 140 b, while in the case of an externalor surface obstruction as, for example, illustrated in FIG. 10B, thereflected power is largely unaffected by the external obstruction.

In a number of embodiments, the detection of magnitude and/or phasechanges associated with porous member resonant frequencies and/ordetection of changes in the porous member resonant frequency may beenhanced through design of the geometry of the chamber coupling thespeaker/microphone system to the porous member. The resonant frequencyof such a system may, for example, be determined by the combinedacoustic impedance of the porous member and acoustic properties of theconnected chamber. Additional detection enhancement may, for example, berealized through selection of the geometry of acoustic ports connectingthe speaker and/or the microphone to the chamber sealed to the porousmember to achieve sympathetic resonance as depicted in FIG. 15A.Alternately or additionally, an acoustic resonant chamber may be affixedto the environmental (external) side of the porous member to enhance thesignal returned to the receiver through the porous member as illustratedin FIG. 15B.

Retroreflective systems as described above offer advantages bypermitting the transmitter and receiver to reside on the same side ofthe porous member. Once again, this arrangement is especially beneficialwhere the porous member is used to separate hazardous or explosiveenvironments on one side (external) from components on the other side(internal) that can be damaged or impaired by the hazardous environmentor represent a potential ignition source to the external environment.However, the detection and discrimination of porous member blockagesusing acoustic signal magnitude and/or phase changes is not limited toretroreflective systems. An alternative is to construct a detectionsystem to directly monitor the acoustic signal transmitted through theporous member. FIG. 16 schematically illustrates an embodiment of such atransmission detection system using a transmitter and receiver locatedon opposite sides of the porous member. Such embodiments may includeadditional barriers or protection components/methods to protect thereceiver from the external environment or to isolate the receiver as anignition source. As described above, intrinsically safe circuitry may beused for the receiver. Added receiver barriers may present theopportunity for blockages to form on the receiver barrier and the porousmember separating the sensor from the ambient environment differently,thereby complicating and potentially impacting the reliability ofdetection of blockages of the porous member. As depicted in FIG. 16, thedetection signal includes a composite of a portion (Irec) of theacoustic signal transmitted through the porous member or barrier (I2)directly to the receiver and acoustic signals reflected and scattered tothe receiver from the surroundings. Thus, blockage detections anddiscrimination are determined from changes in the magnitude and/or phaseof the composite signal at one or more frequencies. Unlike aretroreflective system, it is possible for the blockage to residebetween the porous member and the receiver or beyond the receiver asdepicted in FIGS. 17A and 17B, respectively, requiring different oradditional correlation between the received acoustic signal andblockages to associate changes in the detection system with changes inblockage conditions. Additionally, the discrimination of externalblockage and contamination of the porous member is complicated by thepossibility of blockages absorbing or reflecting at resonant frequenciesof the porous member, potentially complicating detection of changes inporous member transmission as a result of contaminant induced resonancechanges.

Numerous algorithms were tested on the raw data developed using devicesor systems hereof such as device 100 b and testing system 100 b′, andthere are many ways to process the data that will give a signal thatwill change with blockage. In a number of embodiments, an algorithm wasused that was based on a lock-in approach. Both the phase and amplitudeof a signal played over the speaker and received by the microphone willchange when a porous member becomes blocked as described above. Alock-in approach provides both of those outputs with little processing.A lock-in algorithm is, by its nature, a monotone or very narrow banddetector. Detection across multiple frequencies using a single lock-indetector approach requires multiple interrogations in which the acoustictransmitter is excited one frequency at a time. Alternatively, multiplefrequency interrogation can be made with the lock-in by driving thetransmitter at multiple frequencies simultaneously (if such frequenciesare separated sufficiently to discriminate with the lock-in detectorbandwidth) and detecting with parallel lock-in detectors (one for eachfrequency). Multiple frequency interrogation can also be made byrecording the receiver signal and repeatedly passing that signal throughthe lock-in detector, which is locked to each frequency of interestduring each pass. Multi-tone and broad-band interrogation signals may,for example, be used with Fourier-based frequency response functiondetection. Other broadband compatible detection schemes may be used withbroadband or multi-toned techniques. One may also use time domaindetection techniques. Once again, many detection schemes are suitablefor use in the devices, systems and methods hereof. Examples of suitabledetection schemes include, but are not limited to, lock-in algorithms,Fourier transforms, wavelets/curvelets, and the Hilbert transform.

In a number of embodiments, an acoustic wave source or speaker can alsobe used as an acoustic wave sensor in devices hereof. In that regard,changes in sound pressure within the inner chamber of the housingarising from blockage of a porous member can modify the speaker's (wavesource's) acoustic load resulting in distortion and/or other frequencyreferable changes in magnitude and/or phase detectable in changes in theback emf, current or impedance (combined emf and current) at the speakerdrive terminals. Similar to utilization of signals received by amicrophone or receiver separate from the transmitter as discussedelsewhere herein, such measurements and assessments of changes in thespeaker acoustic load can be related to blockage of the porous member.

In addition to sensor output corrections associated with the electronicinterrogation of a sensor as described above, devices and systems hereofmay also be operable to or adapted to apply one or more corrections tosensor output determined as a result of the flow path/blockage test. Inthat regard, sensors may, for example, be thought of as “moleculecounters”. Analytical sensors are thus calibrated in a manner that acertain amount of analyte molecules react at the analytical working orsensing electrode(s) as they diffuse through the instrument and measuredvalues are converted to, for example, a part per million (ppm) orpercentage based equivalent readings based upon previous calibration.When a porous member or barrier associated with a sensor inlet is openand unobstructed, rates of diffusion are very repeatable under the sameconditions. As a porous member becomes blocked or flow paths areotherwise obstructed, the rate at which the molecules can diffuse fromoutside the instrument housing to the sensor can slow, thus lowering therate at which molecules will encounter the active portion of the sensor,and thereby lowering the output. By measuring partial blockages as aresult of one or more tests hereof, one can adjust the sensitivity ofthe sensor to maintain accurate readings regardless of such partialblockages.

Percent blockage may, for example, be readily experimentally correlatedwith a correction factor. An associated lookup table or an associatedalgorithm/formula may, for example, be stored in memory of the deviseand systems hereof, and a correction factor for sensor sensitivity maybe determined therefrom.

The foregoing description and accompanying drawings set forth a numberof representative embodiments at the present time. Variousmodifications, additions and alternative designs will, of course, becomeapparent to those skilled in the art in light of the foregoing teachingswithout departing from the scope hereof, which is indicated by thefollowing claims rather than by the foregoing description. All changesand variations that fall within the meaning and range of equivalency ofthe claims are to be embraced within their scope.

What is claimed is:
 1. A method of detecting at least a partial blockagein a porous member separating an inner chamber of a device comprising agas sensor responsive to an analyte positioned within the inner chamberand an ambient environment, comprising: emitting pressure waves withinthe inner chamber, and measuring a response via a sensor responsive topressure waves positioned within the inner chamber.
 2. The method ofclaim 1 wherein emitting pressure waves within the inner chambercomprises activating a speaker positioned within the inner chamber andmeasuring the response via the sensor responsive to pressure wavescomprises measuring the response via a microphone positioned within theinner chamber.
 3. The method of claim 2 wherein pressure waves areemitted at a plurality of frequencies within the chamber and a responseis measured at more than one of the plurality of frequencies.
 4. Themethod of claim 2 wherein measuring the response comprises measuring atleast one of transmission, reflection or absorbance.
 5. The method ofclaim 4 wherein at least one of a change in amplitude and a change inphase is measured.
 6. The method of claim 4 wherein a change in phase ismeasured.
 7. The method of claim 6 wherein a change in amplitude is alsomeasured.
 8. The method of claim 7 wherein a lock-in algorithm is usedto measure each of the change in amplitude and the change in phase. 9.The method of claim 3 wherein at least one of the plurality offrequencies is a self-resonant frequency of the porous member and aresponse measured at the at least one of the plurality of frequencies isassociable with a blockage that infiltrates pores of the porousmembrane.
 10. The method of claim 2 further comprising using themeasured response to discriminate between at least a partial blockageassociated with an outside surface of the porous member and at least apartial blockage infiltrating pores of the porous member.
 11. The methodof claim 10 wherein pressure waves are emitted at a self-resonantfrequency of the porous member and a response measured at theself-resonant frequency is associated with a determination of the atleast a partial blockage infiltrating pores of the porous membrane. 12.A gas sensor device to detect an analyte gas in an ambient environment,comprising: a housing comprising an inner chamber and a port; a porousmember in operative connection with the port to separate the innerchamber from the ambient environment; a sensor responsive to the analytegas positioned within the inner chamber; a source of pressure wavespositioned within the inner chamber; a sensor responsive to pressurewaves position within the inner chamber; and circuitry in operativeconnection with the sensor responsive to pressure waves to relate aresponse of the sensor responsive to pressure waves to a blockage in theporous member.
 13. The gas sensor device of claim 12 wherein the sourceof pressure waves comprises a speaker and the sensor responsive topressure waves comprises a microphone.
 14. The gas sensor device ofclaim 13 wherein the speaker emits acoustic waves at a plurality offrequencies.
 15. The gas sensor device of claim 14 wherein the circuitrymeasures at least one of transmission, reflection or absorbance.
 16. Thegas sensor device of claim 15 wherein the circuitry measures at leastone of a change in amplitude and a change in phase.
 17. The gas sensordevice of claim 15 wherein the circuitry measures a change in phase. 18.The gas sensor device of claim 17 wherein the circuitry also measures achange in amplitude.
 19. The gas sensor device of claim 16 wherein thecircuitry comprises a processor system in operative connection with amemory system.
 20. The gas sensor device of claim 19 wherein the memorysystem comprises a lock-in algorithm executable by the processing systemto measure each of the change in amplitude and the change in phase. 21.The gas sensor device of claim 14 wherein at least one of the pluralityof frequencies is a self-resonant frequency of the porous member and aresponse measured at the at least one of the plurality of frequencies isassociable with a blockage that infiltrates pores of the porousmembrane.
 22. The gas sensor of claim 13 wherein the circuitry isadapted to use the measured response to discriminate between at least apartial blockage associated with an outside surface of the porous memberand at least a partial blockage infiltrating pores of the porous member.23. The gas sensor of claim 22 wherein pressure waves are emitted at aself-resonant frequency of the porous member and the circuitry isadapted to measure a response at the self-resonant frequency which isassociated with a determination of the at least a partial blockageinfiltrating pores of the porous membrane.